Glycolipids are compounds of importance in therapy. In particular, glycosphingolipids are naturally-occurring compounds found in the membranes of all animal cells and in some plant cells. One such compound is cytolipin H, a pure lipid hapten, which has been isolated from human epidermoid carcinoma extracts.
Cytolipin H is N-lignoceroyl-1-sphingosyl lactoside. This is a compound of formula I (see formulae below) when Q is H, X is --NH--CO--C.sub.23 H.sub.47, Y is --CH.dbd.CH--C.sub.13 H.sub.27 and (sac).sub.m+n, is a lactose residue. A synthesis of such compounds is reported by Nicolaou et al, JACS (1988) 110: 7910-7912, and comprises coupling a protected di- or trisaccharide with a protected sphingosine azide which is then elaborated.
Yu et al, J. Biol. Chem. (1976) 251(1): 198-203, discloses that a sialyltransferase in mouse brain microsomes catalyses the synthesis of sialosylgalactosylceramide from added galactocerebroside and CMP-NANA. The product, i.e. NeuNAc(.alpha.,2-3)gal(.beta.,1-1) cer, and the substrate, are compounds of formulae I and II in which X is --NH--CO--C.sub.12 H.sub.25 and Y is --CH.dbd.CH--C.sub.13 H.sub.27. The enzymatic activity is apparently dependent on the ceramide structure of the glycolipids.
Products of the ceramide type, i.e. containing two hydrophobic residues, have serological activity that depends on the nature of Y; see Graf et al, Chemistry and Physics of Lipids (1974) 13: 367-371.
EP-A-0212400 discloses a chemical synthesis of compounds of formula II wherein n=1, sac is glucopyranose, X is --NH--CO--(C.sub.14-24 alkyl) and Y is --CH.dbd.CH--C.sub.13 H.sub.27 or an analogous group. Intermediates in this synthesis are of the same structure except that X is N.sub.3 or NH.sub.2. The latter is suitable for elaboration to a variety of groups X.
Zimmermann et al, J. Carbohydrate Chem. 7(2): 435-452 (1988), disclose similar compounds, and also analogous compounds wherein n=2. For example, in order to prepare lactosylceramide, the per-O-acetylated trichloroacetimidate of lactose is first coupled with a hydroxysphingosineazide;the product is reduced and elaborated.